Takeoff and reentry of space vehicles creates a hostile environment characterized by high temperatures and turbulence. To protect a space vehicle, heat-sensitive components of the vehicle may be insulated. Without insulation, heat generated by friction as the space vehicle travels at high speed through the atmosphere may damage instruments or structures critical to performance of the space vehicle. A need to protect life and property dictates that sufficient insulation be applied to appropriate portions of space vehicles, to allow the space vehicles to safely launch and return to Earth.
Insulation may be damaged during ground operations, takeoff from Earth, or during flight operations. For instance, a piece of foam insulation broke off the external tank of the Space Shuttle Columbia during takeoff in 2003. The foam insulation piece struck a wing of the space vehicle and damaged the space vehicle's thermal protection system (another form of insulation). It is believed that the damage to the thermal protection system resulted in the disintegration of the Columbia upon reentry and the death of all the astronauts on board. Insulation may also be damaged during preparation for launch, such that repairs must be made in situ (e.g., on the launch pad).
Insulation materials may be selected based upon density, ability to withstand thermal loads, mechanical properties, application methods, toxicity of raw materials, or other properties. For example, an insulation material used to repair damaged insulation of a space vehicle may be selected based on low density, high thermal resistivity, and ability to be formed in situ. For various applications, different properties may be of differing importance. That is, an insulation material deemed appropriate or ideal for one application may be deemed less appropriate or inappropriate for another application.
Ceramics may be used as insulation materials. For example, ceramic tiles having insulating properties may be produced by forming a slurry of ceramic precursors and solids, such as fibers. The slurry may be formed into a mold and placed in an environment of heat and/or vacuum to form a solid ceramic material. Ceramic coatings may also be formed directly on articles requiring insulation. For example, polysilazane resins, such as those sold by Kion Specialty Polymers, of Charlotte, N.C., or Kion Defense Technologies, Inc., of Huntingdon Valley, Pa. (hereinafter, collectively “Kion”), under the trade names HTT 1800 and CERASET® Polysilazane 20, may be combined with a free-radical initiator and applied to surfaces by dipping the surfaces into the resin, or by spraying or brushing resin onto the surfaces. The ceramic coatings may be cured by heating them with or without vacuum, and the required cure time may vary based on the identity and concentration of the initiator and on the cure environment.
Foams, such as polyurethane foams, may be used as insulation materials. Polyurethane foams may be formed by mixing a polyol-based resin with an isocyanate. The components may be mixed as they are sprayed into place, forming the foam. Foams used as insulation may be formed in various shapes, such as in a mold or directly on components to be insulated. Reaction time required for the components to cure may vary based on the selection of the components and the conditions (e.g., temperature) of the mixture.
Fillers may be added during the formation of foams to change properties of the cured foam, such as density, thermal resistivity, modulus of elasticity, etc. Fillers may include particles or microballons of glass, carbon, or ceramic.
Foams may also be formed from polysilazane precursors. For example, polysilazane resins HTT 1800 and CERASET® Polysilazane 20 (Kion) may be mixed with hollow particles to form syntactic foams (foams in which the cells are formed of solid-phase materials, such as microspheres or microballoons). These foams may be molded under vacuum, and may be molded or machined to a desired a shape.